1. Field of the Invention
The present invention relates to a circuit arrangement for shaping an analog read output signal in a rotating mass memory in which write or, respectively, read events are established by a static state signal and a plurality of read heads having assigned preamplifiers is selectively activated with the assistance of a selection signal and is through-connected to a common signal shaping device for further amplification and filtering of the read output signal.
2. Description of the Prior Art
An example of such mass memories is the magnetic disk memory in which a plurality of storage disks are united to form a disk pack arranged in common on a disk drive. The disk pack is motor driven via a disk drive motor having a nominal speed. Combined read/write heads are usually respectively assigned to the active surfaces of the storage disks, these combined read/write heads being moved radially relative to the disk pack by a positioning device for track selection and the positioning device being fashioned as a linear positioner or as a rotary positioner.
In the present state of the art, what is referred to as a head electronics is usually directly three-dimensionally assigned to the individual read/write heads, the head electronics being composed, among other things, of a preamplifier for the read channel or, respectively, of an amplifier output stage for the write channel. In addition to containing actual data disks for the storage of data information, the disk pack can also contain what is referred to as a servo disk on which the servo information for controlling the track setting events for all read/write heads are permanently stored in common. In such a case, a servo head which cooperates with the servo disk is provided in addition to the read/write heads which are assigned to the data disks. As a consequence of the interface conditions which have often already crystallized as a standard for magnetic disk memories and which define a relatively low data transmission rate, it is standard in magnetic disk memories to respectively selectively activate only one of the systems composed of a data disk and a head unit in read or, respectively, write operations. This selection occurs via a common control device which supplies the head electronics of the system to be selected with a corresponding selection signal for activation. This control device is also used to set the corresponding operating state "read" or, respectively, "write" in the disk storage device. To this end, it generates a corresponding static status signal wherein respectively one level is assigned to one of these operating states. In particular, the read and write channels are opened or, respectively, blocked alternatively by way of the status signal.
Given these conditions, it is standard to connect the head of the electronics of the individual data heads in parallel with respect to the read channels or, respectively, write channels and, in particular, to connect the read channels in common to an evaluation circuit which first edits the read and preamplified read output signal, i.e. further amplifies and filters the signal, then digitizes the same and, finally, decodes the signal for the recovery of the binary data signals. In practice, the circuit arrangement for shaping the preamplified analog read output signal contains a controllable differential amplifier as a first signal shaping stage, for which reason the preamplified analog read output signal is likewise supplied to this stage as a difference signal and is usually coupled in via coupling capacitors. The output stages of the preamplifiers of the respective head electronics are, therefore, fashioned as symmetrical amplifiers; they can be emitter followers or they can also be output stages having an open collector. Particularly in the latter case, the two differential signal inputs of the signal shaping device are respectively applied to operating voltage via collector resistors shared by all head electronics.
Systematically conditioned, the signal shaping device with its units such as the controllable differential amplifier and the filter network comprises certain time constants which are required in order to avoid distortions in the analog read output signal. Particularly crucial here are the filter time constants which lie on the order of 30-50 .mu.s given high performance disk storage devices. On the other hand, however, voltage peaks occur at the differential signal inputs of the signal shaping device in switch-over operations, i.e. when switching from the operating state "write" into the operating state "read", this being true both with these voltage peaks effective transient of a considerable chronological length which, given an operating mode of the disk memory having a frequent change from the write state into the read state, and vice versa, leads to a deteriorating performance reduction of the device in the form of relatively long access times.